Abstract : The objective of the project was to conduct a feasibility study on a device to convert millimeter wave images into visible pictures. The planar Fabry-Perot interferometer (FPI) was studied theoretically and experimentally for the passage of millimeter wave beams through it. Experiments showed that millimeter wave images pass through the FPI with little alteration of the intensity profile. The field enhancing effects of the FPI are needed to increase upconversion efficiency of millimeter wave images to visible pictures. Theoretically the passage of an arbitrary field distribution (image) through an FPI can be understood in terms of the transverse modes of the FPI. The diffraction effects were properly included for the various modes in order to obtain the intensity profile at the output. The property of an FPI to act as a spatial band pass filter was pointed out. Experiments were performed to demonstrate spatial filtering characteristics.